12-22-2009, 12:44 PM
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In my view, it's all about dilution of dissolved organics or total dissolved solids. Performing 20 percent water changes dilutes 20 percent of said solids or organics.Performing 50 percent water changes dilutes 50 percent.
With that said however, IF the tanks water change routine had or has been few and far between,, I would perform two to three 20 percent changes in the course of a week rather than large water changes which would suddenly change the chemistry and indeed affect the osmoregulatory functions of the fish. If one begins doing frequent large changes from the beginning or frequent smaller changes (ie) twice or three times a week ,then the fish will tolerate it more easily than infrequent large water changes.
Some sensitive species do not tolerate even moderate changes that happen suddenly but if the total dissolved solids or organics don't ever have a chance to become excessive by performing 20 or 50 percent changes from the outset, then there is little chance of a problem. It is as mentioned,when water changes are few and far btween that fish struggle with sudden change in chemistry even if it is for the better.
Is why most agree that small frequent water changes are better than large infrequent ones.
I change and always have,,25 percent twice a week and 50 percent on the weekend for a total of three changes each week.